The present invention relates to a refractory material, and more in particular to a refractory grain material containing MgO.
In the operation of many high temperature industrial processes, such as basic oxygen steel-making, the use of refractory material containing a large portion of ceramically bonded (dead-burned) crystalline MgO particles (periclase grains) has been increasing due to its ability to withstand the high temperatures typically employed in such furnaces.
Generally, refractory grain MgO is prepared from magnesium compounds as magnesium hydroxide or magnesium carbonate by (a) thermal decomposition of the magnesium compound to form an "activated" MgO, followed by (b) densification of the MgO to form the refractory material. One common method of decomposition and densification involves drying the magnesium compound to remove free water, calcining the magnesium compound at a temperature of from about 500.degree. to about 1100.degree. C. to form the "activated" MgO powder, pressing the MgO powder into pellets, and sintering the pellets at a temperature of about 1500.degree. C. to form refractory grain MgO.
It is well-known that sintering becomes very difficult as the purity of the MgO becomes higher. In order to overcome this difficulty, the level of small amounts of impurities such as lime, alumina, iron oxide, and silica contained in the starting material have been adjusted. While the adjustment of the impurity levels may result in improved sintering, oftentimes it can also have a detrimental effect on the overall refractoriness of the sintered material. In this context refractoriness is defined as the capability of a refractory material to maintain a predetermined degree of chemical and physical identity at high temperatures and in the environment and conditions of use.
A number of prior art processes have attempted to improve the refractoriness of the MgO grains by maintaining a predetermined CaO/SiO.sub.2 ratio and by additions of other refractory oxides of such metals as aluminum, lithium, manganese, potassium, sodium, titanium, vanadium, zirconium and the like. Typical processes are illustrated in U.S. Pat. Nos. 3,540,898 3,582,373, 3,713,855 and 3,754,951.
Although refractory MgO made according to the above processes may show acceptable refractoriness, there is a need in the market place for an improved refractory grain material with a high MgO content and enhanced high temperature compressive strength. These and other desired characteristics are achieved in the present invention.